xfrm: consistently use time64_t in xfrm_timer_handler()

For some reason, blamed commit did the right thing in xfrm_policy_timer()
but did not in xfrm_timer_handler()

Fixes: 386c5680

 ("xfrm: use time64_t for in-kernel timestamps")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>